The present invention pertains to microfabricated electromechanical (MEM) switches which may be fabricated on a substrate.
MEM switches in various forms are well-known in the art. U.S. Pat. No. 5,121,089 to Larson, granted in 1992, describes an example of a MEM switch in which the armature rotates symmetrically about a post. Larson also suggested cantilevered beam MEM switches, in xe2x80x9cMicroactuators for GaAsxe2x80x94based microwave integrated circuitsxe2x80x9d by L. E. Larson et al., Journal of the Optical Society of America B, 10, 404-407 (1993).
MEM switches are very useful for controlling very high frequency lines, such as antenna feed lines and switches operating above 1 GHz, due to their relatively low insertion loss and high isolation value at these frequencies. Therefore, they are particularly useful for controlling high frequency antennas, as is taught by U.S. Pat. No. 5,541,614 to Lam et al. (1996). Such use generally requires an array of MEM switches, and an Nxc3x97N array of MEM switches requires N2+1 output lines and N2 control circuits for direct electrical control. These control lines may need to be shielded to avoid interfering with the high frequency antenna lines, and accordingly add considerable complexity and cost to the fabrication of these switches.
Thus, there exists a need for controlling the MEM switches in such an array by a means which reduces the difficulties imposed by routing control lines.
The present invention alleviates the above-noted problem of providing control lines for an array MEM switches, and provides other benefits as well. In particular, it provides a mechanism for controlling MEM switches with light, with attendant benefits such as isolation, and indeed remoteness, from a controlling light source.
The present invention provides optical control of MEM switches. In a preferred embodiment, two DC bias lines are provided to the vicinity of each MEM switch. On-off control of the switch is then effected by focusing light on the switch substrate. Under illumination, the photo-conductive nature of the semi-insulated substrate causes voltage loss in a series bias resistor to reduce the DC bias voltage applied to the switch. The switches may be used in combination to control an antenna array. Another embodiment of the invention employs a photovoltaic device to provide actuating voltage under illumination, thus obviating all bias lines.